A critical vulnerability in Page Builder CK allows unauthenticated attackers to achieve full remote code execution, triggering urgent CISA intervention.
On July 7, 2026, CISA formally added CVE-2026-56290 to its Known Exploited Vulnerabilities (KEV) Catalog, marking a critical inflection point for the Joomla! ecosystem. The vulnerability exists within the Page Builder CK extension (versions 1.0 through 3.5.x) and allows an unauthenticated actor to execute arbitrary files on the host server. Given the nature of the exploit—which facilitates full Remote Code Execution (RCE)—and the active exploitation status, this vulnerability carries a CVSS 4.0 score of 10.0 (CRITICAL).
The vulnerability is classified under CWE-434: Unrestricted Upload of File with Dangerous Type. The architecture of the Page Builder CK extension failed to implement sufficient server-side validation for incoming file uploads. By circumventing client-side checks or interacting directly with the underlying endpoint, an attacker can bypass intended file type restrictions.
In a standard Joomla! environment, the failure of an extension to sanitize input before passing it to the filesystem allows for the direct upload of executable scripts (e.g., .php files). Once an attacker successfully deposits an executable payload into a web-accessible directory, they can trigger the script through a standard HTTP GET request. The resulting execution inherits the privileges of the web server process (e.g., www-data), granting the attacker persistent unauthorized access, the ability to pivot within the local network, or the capacity to exfiltrate sensitive site configuration data.
The SSVC (Stakeholder-Specific Vulnerability Categorization) assessment classifies this as a CISA Coordinator / 2.0.3 risk, emphasizing its automatable nature and the severity of the total technical impact.
While specific exploit payloads vary depending on the target server environment, the technical entry point relies on the extension’s file-handling logic. Defensive practitioners must audit web server access logs for anomalous POST requests directed at extension-specific upload endpoints. Look for requests that terminate in unexpected file extensions or high-frequency upload attempts occurring outside of authorized administrative sessions.
Because the vulnerability is unauthenticated, traditional session-based access controls are bypassed entirely. Defenders should prioritize implementing network-level ingress filtering to block traffic to known extension-specific paths if the application is not actively undergoing a patch cycle. Furthermore, ensuring that the web server user lacks write permissions to directories that do not strictly require them is a foundational hardening step to limit the impact of such file upload vulnerabilities.
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